In the standard process for making glass containers, certain defects occur due to various process variances. Among these defects, checks are a common type of defect. A check is a crack in the glass that causes a structural flaw in the container. This flaw will likely lead to the container's failure during or after filling. Checks can occur in almost any location on the container. Checks in the finish area and the heel area are detected using several methods. The primary method is to use a directed light source on a specific location on the bottle. A light sensitive sensor is placed such that the check or crack will reflect the directed light into that sensor. Since finish and heel checks occur in repeatable, expected locations, this method works reliably.
Checks that occur in the sidewall area (body) of the container are less repeatable. The process variance that produces such a check, does not cause the check to occur in a repeatable expected location. These checks tend to be large cracks that are curved in shape. They can also be located anywhere on the sidewall of the container.
U.S. Pat. Nos. numbered 3,245,533, 4,399,357 and 4,664,525, disclose check detecting systems.